Rotor for electric generators



Jan. 13, 1942.

W. D. CROCKER ROTOR FOR ELECTRIC GENERATORS Filed Aug. 24, 1940 2Sheets-Sheet l INVENTOR WMZ/,4M 0. VMC/05A BYQM. )4 @mi A TTORNEYParental Jin. 13, 1942 KOTOR FOB ELECTRIC GENERATORS William D. Crocker,Springfield, Mass., signor to American Bosch Corporation, Springfield,Mass., a clwlliion of New York Application August 24, 1940, Serial No.353,993

Claims.

due percentage of rejections in quantity production, notwithstandinginaccuracies and variations in the dimensions of the magnet materialresulting for instance from the casting thereof.

'I'he features of the rotor by which these and other objects areattained will be apparent from the following description taken inconnection with the accompanying drawings which show, as an example, thepreferred form of a bipolar magnet rotor with a plain drive-end bearinghaving the preferred form of lubricating arrangement -in amulti-cylinder magneto.

In the drawings, Fig. 1 is a central vertical section, partly inelevation, of a typical magneto having a magnet rotor and a drive-endbearing therefor in accordance with the invention; Fig. 2 is a sectionalplan view, partly in elevation, of the drive-end bearing on line 2-2 ofFig. l; Fig. 3 is an elevation of the assembled magnet rotor from therear-end thereof; Fig. 4 is a side elevation of the rear-end part of therotor shaft; Fig. 5 is a side elevation, partly in section, of thedrive-end part of the rotor shaft; Fig. 6 is an enlarged sectional viewillustrating a portion of the assembled rotor with a magnet having asubstantially true shaft hole; Fig. '7 is a similar view illustrating amagnet rotor with a nonround shaft hole; Fig. 8 is an enlargedlongitudinal sectional view illustrating a portion of the assembledrotor with a magnet having an axially slanted shaft hole; and Fig. 9 isa similar view with the magnet having a crooked shaft hole.

Referring now to Figs. 1 and 2, the magneto has a flange-mounting frameI, a rotor 2 driven at the drive-end of an engine (not shown) throughappropriate gearing in proper timed relation, a distributor plate 3 anda distributor rotor electrode I driven at a proper speed ratio and intimed relation by the magnet rotor through gearing l and electricallyconnected in well known manner with the high tension terminal t of astationary ignition coil 1. The primary winding of the ignition coil isconnected in well known manner to an interrupter lever (not shown)opened periodically by a cam 8 carried by the rotor in proper timedrelation, the cam either being ground directly on the rotor shaft orbeing a separate ring member, as shown, held in proper position on theshaft in any suitable way.

As best shown in Figs. 1 and 3, the rotor lncludes a bipolar magnet Itof well known form. It may be cast from an alloy containing aluminum,nickel and iron, which besides being so hard as to necessitate grindingin finishing, is so brittle as to readily develop cracks when undulystressed as for instance by forcing a smooth shaft through its shafthole at il, particularly if the shaft hole is distorted as by beingcrooked, slanted or out of round. By the construction herein disclosed,the grinding is reduced considerably and the shaft may be forced intoplace on the true axis of rotation in its bearings without cracking themagnet. 'This reduction in grinding is attained by providing a small hubi2 around the shaft hole at the front face only of the magnet, theremainder of that face and all of the other face of the magnet, as wellas the bounding wall of the shaft hole, being left rough from the mold.The comparatively small annular area of this hub is ground at I3 toprovide a locating surface thereat which is flat or smooth from whichthe magnet is aligned on the shaft, as hereinafter explained,notwithstanding any normal distortion of the shaft hole in the magnetand also notwithstanding any normal departure of the two end faces ofthe magnet from parallelism, due for instance to non-uniform shrinkageupon cooling of the alloy after casting. The rear-end portion I4 of therotor shaft is of cold rolled steel, and to preclude cracking the magnetin being forced through the shaft hole thereof, it is knurledlongitudinally at I5 with the ridges i6 initially peaked and initiallyof slightly greater outside diameter than the true diameter of the shafthole Il (about l0 to 40 thousandths of an inch greater) as indicated inan exaggerated way by the broken lines in Fig. 6. Upon pressing thisknurled portion I5 into the hole Il with the ground surface I3 of themagnet hub I2 held against the work seat of an assembling fixture, andwith the rear-end portion i4 of the rotor shaft fed perpendicularthereinto, some or all of the ridges It are shaved of! by the hardermetal of the magnet as hereinafter described to of the hole Iithroughout a substantial part of the periphery thereof and a substantialpart of the axial length thereof. Flirtingrr ri r eL to prevent thshaft; fronti cockinglthlalfrntgiae the hexagonalportinffl has'alslighty taper at I8 (see Figs. 4, 8 and 9) which results, upon pressurein screwing home the threaded end portionY I9 into the drive-endportiono;yof, thegirotoim shaft, in flattening or otherwise 'deirrning'the edge thereof to an annulariai'ea'of contati-. E'wirft-ltr theabutting rear face of -tiiifiagnet'fljl iveii though that face of themagnet is rough and/or slightly off parallelism with :theflocatingsurface at I3. Upon assembly, the collar 2I nts tightly against thelocating surface I3 of the magnet. The .collar v2i v of greater; puller#diameter than that of the-hubwIZ, welded as indicated sii-22st anumbers@ filetes-around its periphery, in,thepocketor depress formedtherebe-l tween, to securely fasten., thedrive-end.part 20 of the .rotorshaft ,to the magnetl and thereby prevent it from..turningjyitmrespectthereto. It has been found from-prolonged tests that the rear-end partI4 of the rotor shaft does not screw out in service, evenv -Whenthelmagneto iS driven through an impulse coupling because of theconsiderable amount of resistance thereto at the friction v fits inthe-screwthreads connecting the twoshaft parts,aswel l a s -,between theknurls and the bounding wallsof the shaft hole and at the attenedsurfaceofthe hefagon portion Il. If desired, however,therear-endpart of therotor shaft mayy also be welded to the` magnet as shown at 23, orsecuredtothe drive-end shaft. in any other .suitable way.

At .thetimethefro Vs :haft isywelded to the magnet at 22,-the thinsolid-pole-shoes 24, laid atwise over -v the polari Afaces,-4 arefwelded underneath to the-magnet along-theircircumferential surfacesat25. (Fig-5. land-13:) By welding the pole shoes-at-thosegplacesfinsteadof at their front and rear longitudinahends. .as heretofore, theAmiillingofj the endstoffthe pole shoes at 26 tothe predetermined'v edge?distance with. the stator poles 2`Icannoticut-,through -or break atthose -welds, and alsog---thelength andarea, of magnetic 'contact:between-fthe poleshoes and magnet are much increaseds-flhekeyway at 28is milled in the-same setfup. .The ,bearing journals at 29 and 30 are-thenfground-to a high polish,- as well as thettapered surface at 3|.The outer surfaces of lthe polelshoesf 24A are turned to correctdiameter vonf,the ,ax;is, of rrotation of the rotor shaft in itsnhearingr As a result of the foregoingl construction, the grinding -ofthe-magnet,.which may be dicult and expensive on account o f-fhe vextremehardness of the alloy sometimessused is reduced to in the bearingsresulting therefrom, whether the shaft hole is true, or out of round, orslanted or crooked. For instance, in Fig. 6, with the rotor shaft roundthroughout and perpendicular to the locating surface, the entire lengthof the top portions of ridges I6 of the knurled section I 5 are shavedoff uniformly around, and throughout their length, as indicated by thebroken lines. ,with ag-,hon-rtfridisliaft hole the ridges areshavesfoaunequauysround; andthroughout their length, to compensatetherefor. In 'Fig 8, with a slanting shaft hole, the tops of zibeaidgetzarehaved on unequally around at any diameter, and also toprogressively varying 4ents*jalong tli'eaiz'is of the shaft, to campensatcthreforf fInfFig. 9, with a crooked hole,

the tops of the "ridges IB are shaved off to properlycompensatethea'efor. Thus, notwithstanding the exactness or inexactnessof the shaft hole Il vin any such normally cast magnet, the assembledshafta'isedeformedfin assembly around and/or along .the length orallforportions there@Y of to compensa-'terrier .the-distortion of .theshafthole with respectrto'lthe axis-for-center. linev of rotation ofthe'shaftcln fitsrbearings extending through the shaftghole y.of the.magnet ata predetermined ang-leperpendicularly in thisrcase. to thelocating surface II. Furthermore, there is in all thesecases/-a--smoothffriction t'between the deformed:ridgesif5vof-fthe'shaft, or at least some of them-Lorifon-a portion at least ofsome or all of thern'f,":with-:the bounding wall of :the shaftI holeli-,thusuconstitutinga support for the magnet for 'fat',:'leastr-asubstantial x partof vits length betweenfend'faces. f

The foregoing"fac'tos Vcontribute toa reduction in difdcultiesin--theuse' of plain bearings, instead of ballbearlngs,"particularly at thedriveend of the rotor-shaft where' the load is'greatersubstantially.theminimum areadesirable for a locating surfaceg'and thenumber of parts and their weights are so-reduced andsonshed afteryassemblyf that the comparativelylight compact,

rear bearings- 32 ,andlinithe frame I egtend, through the shaftholeJ I:at, substantially .right ISI-setlist there angles to the locating-,sur

icity. gf thegnagis ai minimumamowxsf;

net irirQtatiOa-andfa 9i Wes? due to the Weightof the-magnet and theperiodic magnetic breaks fbetweenf: the magnet and stator polesgA 'Bymeansofthe lubricating :arrangement hereinjdlsclp edyiparticularly inlcombination with tl'ii'sitor have been able to provide a generatorwitlifsucha'plin bearingat vthe drive-end that itisfc'apable{ofoperation without after-long periods 'of opera-j usual.The p' if1 bearlngf"shown at the 'rear an .m1-tight; an@ permanentseal.' 'for therese.

voir. The d iametricallyppposite location ofthe reservoirs in this,wamresultsdn a. propersupply of oil-to the ,bearingin. any .angularposition ofA magneto mounting, and the, oill seal .In vv precludes oilleakage from ythe bearing.. flt has .been .found that withthisvvarrangemnt. the .prope'n amount operating conditions in the fieldand for practically the life of the magneto, with the result thatseizure of the rotor shaft in the bearing is precluded as a practicalmatter at rotor speeds higher than has been usual heretofore with amagneto having a plain bearing at its drive-end. The rear-end bearingand its lubricating means may be the same as at the drive-end bearing.

While I have merely shown the preferred embodiment of this invention, itwill be understood that many modifications thereof are possible withinthe intended broad meaning of the terms of the appended claims. So,also, the invention may be applied to other types of magnetos as Well asto electric generators in general.

Having thus described my invention, what I claim is:

1. In a rotor for generators; a cast permanent magnet having a shafthole which is unmachined for at least a part of its axial length, andalso having a locating surface; and extending through said hole, a shafthaving a knurled section of a material softer than said magnet and of anaxial length of at least the unmachined length of said hole; at least aportion of the top surfaces of said knurled section being deformed, as aresult of being Yforced into said hole and thereby shaved off by saidmagnet, to provide a smooth friction t with the unmachined bounding wallof said hole throughout a substantial part of the periphery thereof anda substantial part of the axial length thereof, and the axis of saidshaft extending through said hole at a predetermined angle to saidlocating surface.

2. In a rotor for generators; a cast permanent magnet having a shafthole which is unmachined for at least a part of its axial length, andalso having a locating surface; and extending through said hole, a shafthaving a longitudinally knurled section of a material softer than saidmagnet and of an axial length of at least the unmachined length of saidhole; at least some of the knurls of said knurled section beingfrusto-conical in cross section for at least a part of the length ofsaid knurled section, as a result of being forced into said hole andthereby shaved off by said magnet, to provide a smooth friction fit withthe unmachined bounding Wall of said hole through a substantial part ofthe periphery face; and extending through said hole, a shaft having aknurled section of a material softer than said magnet and of an axiallength of at least the unmachined length of said hole; at least aportion of the top surfaces of said knurled section being deformed, as aresult of being forced into said hole and thereby shaved off by saidmagnet, to provide a smooth friction t with the unmachined bounding wallof said hole throughout a substantial part of the periphery thereof anda substantial part of the axial length thereof, and the axis of saidshaft extending through said hole perpendicularly to said locatingsurface.

4. In a rotor for generators; a cast permanent magnet having a shafthole which is distorted and which is unmachined for at least a portionof its axial length, and also having an exteriorly projecting hub aroundsaid hole with its radialface machined to form an annular locatingsurface; and extending through said hole, a shaft which has a knurledsection of a material softer than said magnet and of an axial length ofat least the unmachined length of said hole, and which also has acollar, of a diameter greater than said hub, abutting said locatingsurface and welded to said hub in the depression formed therewith; atleast a portion of the top surfaces of said knurled section beingdeformed, as a result of being forced into said hole and thereby shavedoff by said magnet, to provide a smooth friction fit with the unmachinedbounding wall of said hole throughout a substantial part of theperiphery thereof and a substantial part of the axial length thereof,and the axis of said shaft extending through said hole perpendicularlyto said locating surface.

5. In a rotor for generators; a cast permanent magnet having a shafthole which is unmachined for at least a part of its axial length, andalso having a locating surface; and extending through said hole, a shaftwhich has a knurled section of a material softer than said magnet and ofan axial length of at least the unmachined length of said hole, andwhich also has a collar conically tapered with respect to a radial faceof said magnet with at least a portion thereof deformed to an annularring near the periphery of said collar; at least a portion of the topsurfaces of said knurled section being deformed, as a result of beingforced into said hole and thereby shaved off by said magnet, to providea smooth friction fit with the unmachined bounding wall of said holethroughout a substantial part of the periphery thereof and a substantialpart of the axial length thereof, and the axis of said shaft extendingthrough said hole at a predetermined angle to said locating surface.

WILLIAM D. CROCKER.

